100 research outputs found
Variación espacial y estacional de Cianobacterias y sus tasas de fijación de nitrógeno en la BahÃa de Sanya en el Sur del Mar de China
The nitrogen fixation rates of planktonic and intertidal benthic cyanobacteria were investigated in Sanya Bay from 2003 to 2005. Trichodesmium thiebautii was the dominant species of planktonic cyanobacteria during our study. Significant seasonal and spatial variations in Trichodesmium spp. abundance were observed (P<0.01). The highest Trichodesmium concentrations occurred during intermonsoon periods and in the outer region of Sanya Bay (Outer Bay stations). At fixed station S03 the abundance of T. thiebautii ranged from 1.14×103 to 2060×103 trichomes m–2, with an annual mean of 273×103 trichomes m–2. The average nitrogen fixation rate per colony of T. thiebautii was 0.27 nmol N h-1 colony-1 and it did not show any obvious seasonal variations. Nitrogen fixation by planktonic cyanobacteria was highest in the Outer Bay stations, where the estimated amount of new nitrogen introduced by Trichodesmium contributed 0.03 to 1.63% of the total primary production and up to 11.64% of the new production. Statistical results showed that significant seasonal and spatial variations of nitrogen fixation rates were found among the intertidal communities. The main benthic nitrogen-fixing cyanobacteria were identified as members of the genera Anabaena, Calothrix, Lyngbya, Nostoc and Oscillatoria. The highest nitrogen fixation rate was found in microbial mats and the lowest in reefs and rocky sediments. All the benthic communities studied presented their highest nitrogen fixation activity in summer, with an average nitrogen fixation rate of 33.31 µmol N h-1 m-2, whereas the lowest nitrogen activity was detected in winter, with an average nitrogen fixation rate of 5.66 µmol N h-1 m-2. A Pearson correlation analysis indicated that the nitrogen fixation rate of three types of intertidal communities was significantly positively correlated to seawater temperature (P<0.05), whereas only the nitrogen fixation rate of the reefs and rock communities was significantly negatively correlated to seawater salinity (P<0.05).Las tasas de fijación de nitrógeno de cianobacterias intermareales y bentónicas fueron investigadas en la BahÃa de Sanya, desde 2003 a 2005. Trichodesmium thiebautii era la especie dominante de las cianobacterias planctónicas durante nuestra investigación. Se observaron variaciones espaciales y estacionales significativas (P<0.01) en la abundancia de Trichodesmium spp. La concentración más elevada de Trichodesmium se observó durante los perÃodos de intermonzón y en la región exterior de la BahÃa de Sanya (estaciones fuera de la BahÃa). En la estación fija S03 la abundancia de T. thiebautii variaba desde 1.14×103 a 2060×103 tricomas m–2, con una media anual de 273×103 tricomas m–2. El promedio de la tasa de fijación de nitrógeno por colonia de T. thiebautii era de 0.27 nmol N h-1 colonia y no mostraba una clara variación estacional. La fijación de nitrógeno por las cianobacterias planctónicas era superior en las estaciones de fuera de la BahÃa, donde la cantidad estimada de nitrógeno nuevo introducido por Trichodesmium contribuÃa del 0.03 al 1.63% del total de la producción primaria y hasta el 11.64% de la producción nueva. EstadÃsticamente los resultados mostraban que las variaciones espaciales y estacionales significativas de las tasas de fijación de nitrógeno fueron encontradas entre las comunidades intermareales. Las principales cianobacterias bentónicas fijadoras de nitrógeno fueron identificadas como miembros de los géneros Anabaena, Calothrix, Lyngbya, Nostoc y Oscillatoria. La tasa de fijación de nitrógeno más alta fue encontrada en los tapetes microbianos y las más bajas en los arrecifes y sedimentos rocosos. Todas las comunidades bentónicas estudiadas presentaban la mayor actividad de fijación de nitrógeno en verano, con un promedio de tasas de fijación de 33.31 ?mol N h-1 m-2, mientras que la menor actividad de fijación de nitrógeno fue detectada en invierno, con un promedio de 5.66 ?m N h-1 m-2. Análisis de correlación (Pearson) indicaban que las tasas de fijación de nitrógeno en los tres tipos de comunidades intermareales estaban significativamente correlacionados con la temperatura del agua (P<0.05). Mientras que la tasa de fijación de nitrógeno de las comunidades de los arrecifes y sedimentos rocosos estaban correlacionadas significativamente con la salinidad del agua de mar (P<0.05)
Distribución del fitoplancton y su relación con variables ambientales en Sanya Bay, mar del Sur de la China
Phytoplankton quantification was conducted in Sanya Bay from January 2005 to February 2006. A submersible in situ spectrofluorometer, which permits the differentiation of four algal groups (green algae, diatoms and dinoflagellates, cryptophytes and cyanobacteria) was used. Seasonal variation of total chlorophyll a concentration showed that high value appeared in summer and low concentration occurred in spring. Diatoms and dinoflagellates group was the predominant phytoplankton all year in the Bay. The stable stratification of phytoplankton vertical distribution came into being in July. During the stratification event, the total chlorophyll a concentration of deep layer was much higher than the surface; cyanobacteria and cryptophyta groups decreased and almost disappeared, however, the concentration of green algae and diatoms and dinoflagellates groups increased. In deep layer, the concentration of diatoms and dinoflagellates group increased sharply, which was about eight times more than that in the surface layer. The vertical profiles character of phytoplankton showed that from inshore stations to outer bay the stratification of phytoplankton vertical distribution gradually strengthened. Dissolved inorganic nutrient especially phosphate and inorganic nitrogen and cold-water upwelling were the main regulating factor for phytoplankton distribution.Desde enero 2005 a febrero 2006, en Sanya Bay se llevó a cabo la cuantificación del fitoplancton. Para ello se usó un espectrofotómetro sumergible in situ que permitÃa la diferenciación de cuatro grupos de algas (algas verdes, diatomeas y dinoflagelados, criptofitas y cianobacterias). La variación estacional de la concentración de clorofila a, mostraba que los valores altos aparecÃan en verano y los bajos en invierno. Durante todo el año el grupo de fitoplancton predominante era el de dinoflagelados y diatomeas. La estratificación estable de la distribución vertical del fitoplancton aparecÃa en julio. Durante la estratificación la concentración total de la clorofila a de la capa profunda era más alta que en la superficie; los grupos de crisófitas y cianobacterias decrecÃan hasta casi desaparecer, sin embargo la concentración de algas verdes y diatomeas se incrementaba. En la capa profunda la concentración del grupo formado por diatomeas y dinoflagelados se incrementaba considerablemente con concentraciones ocho veces más elevadas que en la superficie. El carácter de los perfiles verticales de fitoplancton desde las estaciones costeras hasta fuera de la BahÃa aparecÃa gradualmente más definido. Los nutrientes inorgánicos correspondientes a fósforo y nitrógeno junto con la subida de agua frÃa eran los factores principales que regulaban la distribución del fitoplancton
Estructura de la comunidad bacteriana en sedimentos de manglares en relación a variables medioambientales mediante análisis de fragmentos del gen 16S rRNA y electroforesis en geles desnaturalizantes
Bacterial community structure and the relationship between environmental variables and microbial communities in the surface sediments of tropical mangrove ecosystems were investigated in Sanya, Hainan Island, China. Profiles of bacterial communities were generated using culture-independent PCR-denaturing gradient gel electrophoresis (DGGE), and the results were interpreted with multivariate statistical analysis. Findings suggested that microbial communities varied with sample collection sites and seasons. The samples collected from the same sample sites at the same time had more similar microbial communities except samples SH3 and AB5, which also had unique sediment quality. Canonical correspondence analysis (CCA) revealed that the organic carbon concentration of the sediments accounted for a significant amount of the variability in the bacterial community composition. Phylogenetic analysis was used to identify the major groups of the predominant bacterial phylotypes. 16S rRNA gene-V3 fragments from 17 individual DGGE bands were sequenced and the corresponding bacteria were found in mangrove sediments for the first time based on BLAST results. Predominant bacterial phylotypes clustered with various taxonomic groups, including Proteobacteria, Bacteroidetes, Gemmatimonadetes, Actinobacteria and Firmicutes.La estructura de la comunidad bacteriana y la relación entre variables ambientales y las comunidades microbianas de la superficie de sedimentos de los ecosistemas tropicales de manglares fueron investigados en Sanya, Hainan Island, China. Los perfiles de las comunidades bacterianas fueron obtenidos utilizando electroforesis de gradiente de gel desnaturalizante (DGE), cultivo-independiente, y los resultados fueron interpretados con un análisis estadÃstico multivariante. Los resultados sugerÃan que las comunidades microbianas variaban con los lugares de muestreo y las estaciones. Las muestras recogidas en el mismo lugar de muestreo y al mismo tiempo tenÃan comunidades microbianas similares, excepto las muestras SH3 y AB5, que tenÃan diferente calidad de sedimentos. El análisis de correspondencia (CCA) mostró que la concentración de carbono orgánico en sedimentos explicaba una parte importante de la variabilidad en la composición de la comunidad bacteriana. Los análisis filogenéticos fueron usados para identificar los grupos más importantes de filotipos predominantes de bacterias. Se secuenciaron fragmentos 16 rRNA gene-V3 de 17 bandas individuales de DGE y las bacterias correspondientes fueron encontradas por primera vez en sedimentos de manglares en base a resultados de BLAST. Los filotipos de bacterias predominantes se agrupaban con varios grupos taxonómicos que incluyen Proteobacteria, Bacteroidetes, Gemmatimonadetes, Actinobacteria y Firmicutes
Solvable dilation model of -symmetric systems
The dilation method is a practical way to experimentally simulate
non-Hermitian, especially -symmetric quantum systems. However, the
time-dependent dilation problem cannot be explicitly solved in general. In this
paper, we present a simple yet non-trivial exactly solvable dilation problem
with two dimensional time-dependent -symmetric Hamiltonian. Our system
is initially set in the unbroken -symmetric phase and later goes
across the so-called exceptional point and enters the broken -symmetric phase. For this system, the dilated Hamiltonian and the evolution
of -symmetric system are analytically worked out. Our result clearly
showed that the exceptional points do not have much physical relevance in a
\textit{time-dependent} system.Comment: 9 pages, 4 figures, close to the published versio
Simplifying Low-Light Image Enhancement Networks with Relative Loss Functions
Image enhancement is a common technique used to mitigate issues such as
severe noise, low brightness, low contrast, and color deviation in low-light
images. However, providing an optimal high-light image as a reference for
low-light image enhancement tasks is impossible, which makes the learning
process more difficult than other image processing tasks. As a result, although
several low-light image enhancement methods have been proposed, most of them
are either too complex or insufficient in addressing all the issues in
low-light images. In this paper, to make the learning easier in low-light image
enhancement, we introduce FLW-Net (Fast and LightWeight Network) and two
relative loss functions. Specifically, we first recognize the challenges of the
need for a large receptive field to obtain global contrast and the lack of an
absolute reference, which limits the simplification of network structures in
this task. Then, we propose an efficient global feature information extraction
component and two loss functions based on relative information to overcome
these challenges. Finally, we conducted comparative experiments to demonstrate
the effectiveness of the proposed method, and the results confirm that the
proposed method can significantly reduce the complexity of supervised low-light
image enhancement networks while improving processing effect. The code is
available at \url{https://github.com/hitzhangyu/FLW-Net}.Comment: 19 pages, 11 figure
- …